Adaptive loading for orthogonal frequency division multiplex (OFDM) communication systems

ABSTRACT

An orthogonal frequency division multiplex (OFDM) transmitter may adaptively load each sub-carrier, buffering less than an OFDM frame in order to reduce hardware requirements and latency. The transmitter may use feedback information from the receiver regarding the quality of the sub-carriers. In addition, combining repetition and puncturing to achieve a desired date rate per class further reduces hardware by simplifying or even eliminating an interleaver. Additional mitigation and even performance enhancement techniques are incorporated to address inter-class boundaries within an OFDM frame, such as introducing transition classes. Channel state information may be reported in various formats including full bitmap, changed subchannels, and reported bad subchannels.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present application for patent claims priority to ProvisionalApplication Ser. No. 61/103,762, entitled “Adaptive Loading forOrthogonal Frequency Division Multiplex (OFDM) Communication Systems,”filed Oct. 8, 2008, assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

FIELD OF INVENTION

The present description relates generally to data communications, andmore specifically to techniques for adaptive loading in an orthogonalfrequency division multiplexing (OFDM) communication system.

BACKGROUND

Wireless communication systems employ various types of modulationschemes. Typically, a modulation scheme may be selected based upon therequirements of the particular system. Orthogonal Frequency DivisionMultiplex (OFDM) is a modulation scheme that has a primary advantageover single-carrier schemes in that it has an ability to cope withsevere channel conditions.

In an OFDM system, the system bandwidth is effectively partitioned intoa number (N_(F)) of frequency subchannels that may be referred to assub-bands, sub-carriers, or frequency bins. Each frequency subchannel isassociated with a respective frequency tone. Typically, the transmitteddata is encoded with a particular coding scheme to generate encodedbits. The encoded bits may be further grouped into multi-bit symbolsthat are mapped to modulation symbols based on a particular modulationscheme (e.g., M-PSK or M-QAM). The serial data comprising the mappedmodulation symbols are then turned into parallel data symbols with aspecific time duration. These parallel data symbols are transformed byan Inverse Fast Fourier Transform (IFFT), which in turn generates themodulation of the data onto the various sub-carriers. The datatransmitted on the sub-carriers for each time interval is commonlycalled an OFDM symbol. Thus, information is transmitted on more than onecarrier, which in turn provides frequency diversity and adds robustness.

Nevertheless, each frequency subchannel of an OFDM system may experiencedifferent channel conditions (e.g., different fading and multipatheffects) and signal-to-noise-and-interference ratios (SNIRs). Thus, themodulation symbols that collectively form a particular data packet maybe individually received with different SNIR values. As a result, thesupported data rates for the frequency subchannels may also vary overtime. Thus, it may be inefficient to transmit data at the same data rateand/or transmit power for all of the given subchannels. In conjunction,it may be challenging to effectively code and modulate data efficientlyfor an adaptive loading OFDM system, because of the dynamic transmissionparameters. A system that utilizes fixed transmission parameters in someaspects may be simpler to code and modulate, but may be more susceptibleto inefficient transmission. Such a system may be Ultra Wide-Band (UWB).

UWB typically transmits each sub-carrier equally loaded with no carrierquality knowledge at the transmitter. Essentially, UWB keeps the averagedata rate constant. Diversity, and hence interleaving, becomes moreimportant in UWB in order to reduce the chances of losing an informationbit. However, equally loading the sub-carriers under-utilizes highquality sub-carriers and may require medium access channel (MAC)mitigation of data losses due to time varying changes in channelconditions.

Therefore, there is a need in the art to provide solutions to the aboveidentified problems.

SUMMARY

The following simplified summary provides a basic understanding of someparts of the disclosed aspects and is intended to neither identify keyor critical elements nor delineate the scope of such aspects. Itspurpose is to present some concepts of the described features in asimplified form as a prelude to the more detailed description that ispresented later. The various aspects disclosed herein are directed to amethod and an apparatus for adaptive loading in an orthogonal frequencydivision multiplexing (OFDM) communication system.

In some aspects, a method is provided in which sub-carriers are groupedinto at least one of a plurality of classes. The grouping is based uponfeedback and each class has an associated data rate. Encoded data bits,sized less than an OFDM frame, are de-multiplexed in order to correspondto the classes. The encoded data bits are rate adapted in order tocorrespond to the class' associated data rate. The rate adapted databits are buffered according to the classes, and each class has anassociated buffer. Finally, the buffered data is mapped onto thecorresponding group of sub-carriers for data transmission.

In yet another aspect, a method is provided in which received OFDMsymbols are de-mapped in order to produce rate adapted bits from atleast one of a plurality of sub-carriers; each sub-carrier has anassociated class and each class has an associated data rate. Thesub-carriers are grouped into at least one of a plurality of classes,and the grouping is based upon channel state information. Then rateadapted data bits are buffered according to the classes, and each classhas an associated buffer. Finally, in order to produce encoded databits, the buffered rate adapted data bits are multiplexed; themultiplexing comprises rate adapting the rate adapted data bits, sizedless than an OFDM frame, corresponding to their classes.

In an aspect, an apparatus is provided in which there are means forgrouping sub-carriers into at least one of a plurality of classes andthe grouping is based upon feedback and each class has an associateddata rate. There are means for de-multiplexing encoded data bits, sizedless than an OFDM frame, to correspond to the at least one of aplurality of classes and the encoded data bits are rate adapted in orderto correspond to the class' associated data rate. There are means forbuffering the rate adapted data bits according to the at least one of aplurality of classes and each class has an associated buffer. Finally,there are means for mapping the buffered data onto the correspondinggroup of sub-carriers for data transmission.

In yet another aspect, an apparatus is provided in which there are meansfor de-mapping a received OFDM symbol from at least one of a pluralityof sub-carriers in order to produce rate adapted bits, and eachsub-carrier has an associated at least one of a plurality of classes.There are means for grouping the at least one of a plurality ofsub-carriers into at least one of a plurality of classes; the groupingis based upon channel state information and each class has an associateddata rate. There are means for buffering the rate adapted data bitsaccording to the at least one of a plurality of classes, and each classhas an associated buffer. Finally, there are means for multiplexing therate adapted bits, sized less than an OFDM frame, corresponding to theat least one of a plurality of classes; the rate adapted data bits arerate adapted in order to produce encoded data bits.

In some aspects, an apparatus is provided in which a grouping module isconfigured to group sub-carriers into at least one of a plurality ofclasses. The grouping is based upon feedback, and each class has anassociated data rate. A de-multiplexing module is configured tode-multiplex encoded data bits, sized less than an OFDM frame, tocorrespond to the at least one of a plurality of classes, and theencoded data bits are rate adapted in order to correspond to the class'associated data rate. A buffering module is configured to buffer therate adapted data bits according to the at least one of a plurality ofclasses; each class has an associated buffer. Finally, a mapper moduleis configured to map the buffered data onto the corresponding group ofsub-carriers for data transmission.

In yet another aspect, an apparatus is provided in which a de-mappingmodule is configured to de-map a received OFDM symbol from at least oneof a plurality of sub-carriers in order to produce rate adapted bits,and each sub-carrier has an associated at least one of a plurality ofclasses. A grouping module is configured to group the at least one of aplurality of sub-carriers into at least one of a plurality of classes.The grouping is based upon channel state information, and each class hasan associated data rate. A buffering module is configured to buffer therate adapted data bits according to the at least one of a plurality ofclasses; each class has an associated buffer. Finally, a multiplexingmodule is configured to multiplex the rate adapted bits, sized less thanan OFDM frame, corresponding to the at least one of a plurality ofclasses; the rate adapted data bits are rate adapted in order to produceencoded data bits.

In another aspect computer program product is provided in which acomputer-readable medium comprises code for causing a computer to groupsub-carriers into at least one of a plurality of classes. The groupingis based upon feedback, and each class has an associated data rate. Tode-multiplex encoded data bits, sized less than an OFDM frame, tocorrespond to the at least one of a plurality of classes. The encodeddata bits are rate adapted in order to correspond to the class'associated data rate. To buffer the rate adapted data bits according tothe at least one of a plurality of classes; each class has an associatedbuffer. Finally, to map the buffered data onto the corresponding groupof sub-carriers for data transmission.

In yet an aspect, a computer program product is provided in which acomputer-readable medium comprises code for causing a computer to de-mapa received OFDM symbol from at least one of a plurality of sub-carriersin order to produce rate adapted bits, and each sub-carrier has anassociated at least one of a plurality of classes. To group the at leastone of a plurality of sub-carriers into at least one of a plurality ofclasses. The grouping is based upon channel state information, and eachclass has an associated data rate. To buffer the rate adapted data bitsaccording to the at least one of a plurality of classes; each class hasan associated buffer. Finally, to multiplex the rate adapted bits, sizedless than an OFDM frame, corresponding to the at least one of aplurality of classes, wherein the rate adapted data bits are rateadapted in order to produce encoded data bits.

In some aspects, an integrated circuit is provided in which a processoris operable to group sub-carriers into at least one of a plurality ofclasses. The grouping is based upon feedback and each class has anassociated data rate. The processor is operable to receive feedback, andde-multiplex encoded data bits, sized less than an OFDM frame, tocorrespond to the at least one of a plurality of classes. The encodeddata bits are rate adapted in order to correspond to the class'associated data rate. Is operable to buffer the rate adapted data bitsaccording to the at least one of a plurality of classes; each class hasan associated buffer. Is operable to map the buffered data onto thecorresponding group of sub-carriers for data transmission. The processoralso has memory associated with it.

In yet another aspect, an integrated circuit is provided in which aprocessor is operable to de-map a received OFDM symbol from at least oneof a plurality of sub-carriers in order to produce rate adapted bits.Each sub-carrier has an associated at least one of a plurality ofclasses. Is operable to group the at least one of a plurality ofsub-carriers into at least one of a plurality of classes. The groupingis based upon channel state information and each class has an associateddata rate. The processor is operable to buffer the rate adapted databits according to the at least one of a plurality of classes; each classhas an associated buffer. Is operable to multiplex the rate adaptedbits, sized less than an OFDM frame, corresponding to the at least oneof a plurality of classes. The rate adapted data bits are rate adaptedin order to produce encoded data bits. Finally, the processor isoperable to transmit a channel state information (CSI) report. Theprocessor also has memory associated with it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a basic diagram of a wireless communication systemthat may be used to operate the various aspects disclosed;

FIG. 2 illustrates a simplified block diagram of a transmitter andreceiver that may be used to operate the various aspects disclosed;

FIG. 3 illustrates a more detailed block diagram of a transmitter andreceiver that may be used to operate the various aspects disclosed;

FIG. 4 illustrates a more detailed block diagram of a wirelesscommunication system that may be used to operate the various aspectsdisclosed;

FIG. 5 illustrates a process for transmitting adaptive loaded data in anaspect of the design;

FIG. 6 illustrates a process for receiving data that was adaptive loadedin an aspect of the design;

FIG. 7 illustrates an example of an apparatus that performs adaptiveloading for transmission with an aspect of the design;

FIG. 8 illustrates an example of an apparatus that receives informationtransmitted by an adaptive loading transmitter with an aspect of thedesign.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. It should be apparent thatthe teachings herein may be embodied in a wide variety of forms and thatany specific structure, function, or both being disclosed herein ismerely representative. Based on the teachings herein one skilled in theart should appreciate that an aspect disclosed herein may be implementedindependently of any other aspects and that two or more of these aspectsmay be combined in various ways. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, such an apparatus may be implemented orsuch a method may be practiced using other structure, functionality, orstructure and functionality in addition to or other than one or more ofthe aspects set forth herein.

The various aspects disclose a method and an apparatus for adaptiveloading in an orthogonal frequency division multiplexing (OFDM)communication system in order to solve the various problems statedabove. The features, nature, and advantages of the present disclosurewill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings.

FIG. 1 illustrates a basic diagram of a wireless communication system 10that may be used to operate the various aspects disclosed. The wirelesscommunication system 10 may be an ad hoc wireless communication networkand may support peer-to-peer communications. During peer-to-peercommunication, nodes, devices, terminals or stations may communicatedirectly with each other, as opposed to using base stations, accesspoints, and/or access routers to relay or forward communications. Insome such networks, devices within the network may relay or forwardtraffic destined to other devices. Some ad hoc networks may include bothterminals and access points.

Network 10 may include any number of mobile devices or nodes, of whichsix are illustrated, that support wireless communication. Mobile devicesmay be, for example, cellular phones, smart phones, laptops, handheldcommunication devices, handheld computing devices, satellite radios,global positioning systems, PDAs, and/or any other suitable device forcommunicating over wireless communication system 10. Nodes, as usedherein, include mobile devices, access points, base stations, accessrouters, or the like.

Nodes 2, 4, 5, 6, 7, and 8 are illustrated as configured in apeer-to-peer ad hoc topology. Each node may be within range of one ormore other nodes and may communicate with the other nodes or throughutilization of the other nodes, such as in a multi-hop topology (e.g.communications may hop from node to node until reaching a finaldestination). For example, a sender node 2 may wish to communicate withreceiver node 8. To enable packet transfer between sender node 2 andreceiver node 8, one or more intermediate nodes 4, 6, 5, and 7 may beutilized. It should be understood that any node 2-8 may be a sender nodeand/or a receiver node and may perform functions of either sending orreceiving information at substantially the same time (e.g., maybroadcast or communicate information at about the same time as receivinginformation). It should also be understood that any node 2-8 could alsoprovide access to other communications infrastructure, such as a wirednetwork (not shown), and in some cases may function similar to an accesspoint. A node may utilize one or more antennas. The multiple accesswireless communication system 10 may utilize OFDM. FIG. 2 illustrates asimplified block diagram of a wireless communication system 10 thatcomprises a transmitter and receiver that may be used to operate thevarious aspects disclosed.

In an aspect, FIG. 2 shows a communication system 100 that may utilizeOFDM-based UWB and perform adaptive loading and other performanceenhancements. The communication system 100, for simplicity shows onlyone transmitter device 102 and receiver device 104. However, typicallymultiple transmitter devices and receiver devices are part of acommunication system. Moreover, a single communication device (e.g., acell phone or laptop) may comprise both the functionality of thetransmitter device 102 as well as the receiver device 104. In order toperform adaptive loading, first the sub-carriers are grouped intoclasses C_(i) of quality levels. The sub-carriers may be grouped basedon feedback from the receiver device 104. For example, the receiverdevice 104 may send channel state information (CSI) to the transmitter102. Once the sub-carriers are grouped into classes, a constant optimaldata rate R_(i) is then associated with the classes. Information bitsmay first be encoded then rate adapted R_(i), modulated, and finallytransmitted on the characterized sub-carriers according to their classC_(i).

In an aspect of the design, information bits 106 are sent to a baselineencoder 108. The information bits may be partitioned into packets orframes, and each packet may be individually processed and transmitted.The coding performed by the encoder 108 increases the reliability of thedata transmission. The coding scheme encoder 108 may utilize may be anycombination of CRC (cyclic redundancy check) coding, convolutionalcoding, Turbo coding, block coding, other coding, or no coding at all.In an aspect of the design, for each packet, the data in the packet maybe used to generate a set of CRC bits, which may be appended to thedata. The data and CRC bits may then be coded with a rate ⅓convolutional code or a Turbo code to generate the encoded data for thepacket. Once encoded, the encoded bits are then sent to a rate adapter112.

A mapper 110 b may get CSI feedback information from 110 a. The mapper110 b uses the CSI feedback information to generate the mapping betweensubcarriers and classes (buffers). The rate adapter 112 will change theencoded bits data rate to match the sub-carrier class' data rates. Forexample, one class C₇ may comprise strong carriers and have a data rateof R₇. In this example, the rate adapter will change the encoded databits rate to be R₇. Moreover, a class C₀ may comprise weak carriers andhave a data rate of R₀. For this class, the rate adapter would thenchange the encoded data bits rate to be R₀. In order to accomplish this,the rate adapter 112 may utilize puncturing or repetition.

In an aspect of the design, the rate adapter 112 first uses repetitionon the encoded bits then applies puncturing. This pattern may providesome system gain in that adjacent subcarriers may be less affecting by acenter band fade. There may be any number of levels of classes definedby the system. In an aspect of the design, eight (8) classes aredefined. The rate adapter 112 may eliminate the need for an interleaver114. However, header information may still need to be interleaved. Thus,in an aspect of the design a header may be transmitted at a fixed 53.3Mbps with some interleaving provided by the optional interleaver 114.This may allow a reduction in size of the interleaver 114 to perhaps one(1) to three (3) OFDM symbols (i.e., 200-600 bits) without having to dofrequency or time spreading but rather a simple repetition of four (4).The rate adapter 112 may be part of a de-multiplexer wherein the encodedbits are MUXed to the various subchannel classes. The de-multiplexer mayalso include a buffer, or several buffers, that correspond to theclasses C_(i) in order to hold the rate adapted bits for a mapper 110 bto map them onto a corresponding subchannel. The buffer or buffers mayalso be separate from the de-multiplexer. In an aspect of the design,for each class C_(i), a class buffer of coded bits may be maintained.Thus, a rate adapter 112 using repetition or puncturing may fill up theclass buffer. The mapper 110 b may empty the buffer. When the classbuffer is empty, more bits may be requested. The operation may beentirely deterministic in that a receiver is able to reproduce the exactsame pattern as the transmitter at the receiver. Therefore, a predictionmay be made as to sizes of data chunks being sent.

Once the data is rate adapted and/or interleaved, it may be passed on toa modulator 116. The rate adapted bits may be modulated by the modulator116. One or more modulation schemes may be used for the frequencysubchannels, as indicated by the modulation control. For each modulationscheme selected for use, the modulation may be achieved by grouping setsof received bits to form multi-bit symbols and mapping each multi-bitsymbol to a point in a signal constellation corresponding to theselected modulation scheme (e.g., QPSK, M-PSK, M-QAM, or some otherscheme). The mapper 110 b will map the symbols from each class onto thecorresponding sub-carriers.

The mapper 110 b may be dynamic in nature, because the sub-carriers maychange classes based on varying channel conditions. The mapper 110 b maybe implemented in various ways. In an aspect of the design, the mapper110 b may be implemented as a dynamic look up table residing in a randomaccess memory (RAM). Each mapped signal point corresponds to amodulation symbol. Symbol mapping may provide a vector of (up to N_(F))modulation symbols for each transmission symbol period. The number ofmodulation symbols in each vector corresponds to the number of (up toN_(F)) frequency subchannels selected for use for that transmissionsymbol period. The mapper 110 b maps the modulated symbols onto thecorresponding sub-carriers via an IFFT 118, and transmits them via alocal transmitter and antenna 120. Only one transmitting and receivingantenna are shown, but more than one antenna can be used fortransmission and reception (e.g., MIMO or SIMO). The OFDM transmissionis received over-the-air (OTA) at the receiver device 104 by a localreceiver and antenna 122.

The receiver device 104 performs a complimentary process to that of thetransmitter device 102. A de-mapper 126 passes the received informationthrough a Fast Fourier Transform (FFT) 124 in order to obtain modulationsymbols from the sub-carriers. The de-mapper further controls thereceiving processes, specifically a demodulator 128, a deinterleaver130, and a rate adapter 132. In an aspect of the design, the rateadapter 132 concatenates the various data rates, as well as removingpuncturing and repetition that were used to achieve the desired datarate. Then the results pass through a baseline decoder 134 to reproduceinformation bits 136. At the receiver device 104, the same logic may beused to read the appropriate buffer (class) in the appropriate order.The ordering may appear to be semi-random due to the difference in theamount of tones belonging to each class; however, it is possible todetermine the reproducible order. In an aspect of the design, a methodmay include counting the number of tones per one (1) or two (2) OFDMsymbols needed per class, and filling up that class with the amount ofbits needed. In the case where a class remains partially unfilled in thelast OFDM symbol, it is merged with a lower quality class. Then theclasses are processed by a determined sorting order.

In an aspect of the design, both the transmitter device 102 and thereceiver device 104 may have the same quality class knowledge. Hence, itmay be sufficient to apply the same algorithm at transmitter device 102and receiver device 104 in order to properly MUX/deMUX bits betweenencoded coded stream and classes, and to properly map/unmap bits betweenclasses and sub-carriers. At the receiver device 104, the coded streammay incur un-puncturing or un-repetition before it goes into a decoder134. Un-puncturing means that the absent metric is replaced by valuezero (0). Un-repetition means to accumulate repeated metrics. A numberof performance enhancements may mitigate or enhance the communicationsystem 100 beyond any performance detriments that may be introduced bythe simplified hardware architecture. FIG. 3 helps illustrate aspects ofthe design that incorporates some of these techniques.

FIG. 3 illustrates a more detailed block diagram of a communicationsystem 200 that comprises a transmitter and receiver that may be used tooperate the various aspects disclosed. Communication system 200 performsOFDM transmission between an adaptive loading transmitter 202 andreceiver 204. Adaptive loading may cause a mixing of different ratecodes. The classes and corresponding rates may be based on the Signal toNoise and Interference Ratio (SINR) that may be measured at the adaptiveloading receiver 204. Each class is characterized by a constant datarate R_(i). The data rate may be tuned to the corresponding SINR. In anaspect, the information bits 206 are data processed by a one third (⅓)rate convolutional encoder 208 to produce encoded bits 210. However, theencoder 208 could use other rates and other types of encoding schemes.The encoded bits 210 pass to a de-multiplexer (MUX) 212 for dataprocessing to achieve a desired data rate in accordance with a classselector 214, which advantageously may impose boundary mitigation 216.

The de-multiplexer 212 feeds encoded bits 210 to a plurality of rateadapting elements 217 a-217 c that produce the assigned data rate. In anaspect of the design, the repetition and puncturing patterns produced bythe rate adapting elements 217 a-217 c are relatively similar in orderto avoid significant performance degradation due to the boundariesbetween classes. The channel conditions vary and so the rate forchannels may vary. As a result, the class selector 214 may direct thede-multiplexer 212, for example, to start at a ⅓ rate code, then jump toa ½ rate code, then to a ⅝ rate code, then back again to a ⅓ rate code.

The rate adapted bits are then moved from the rate adapting elements 217a-217 c into class buffers of buffer 218. In an aspect of the design,buffer 218 may be one buffer that is partitioned into smaller buffers219 a-219 c, which may be less expensive than having one buffer perclass. The buffer 218 may also comprise several individual discreetbuffers. In an aspect of the design, buffer 218 is depicted as a unitarymemory component segregated into the plurality of class buffers {C₀,C_(i), . . . , C_(N−1)} 219 a-219 c. Each buffer 219 a-219 c is sizedless than an OFDM frame. Each class owns a section in the buffer withdynamic size. The more tones in the class, the larger the buffer size.

In one aspect of the design, all classes have a size that is a multipleof the puncturing patterns. Each class buffer may be filled and then thenext class buffer may be filled. At the adaptive loading receiver 204,the opposite function may be performed and the receiving class buffersmust be full before being read sequentially by a de-mapper. If it isdifficult or undesirable to make the size of the classes multiplepuncturing patterns, then additional techniques may be employed. Forexample, some extra tones may be dropped to the lower classes untilmultiples are achieved. Alternatively, additional small pre-bufferingmay be employed for particularly demanding classes.

When a class buffer 219 a-c is empty, a request 220 from buffer 218 orfrom the tone mapper 222 may be made for the de-multiplexer 212 toprovide more bits. The tone mapper 222 maps the class buffers 219 a-219c of buffer 218 to an Inverse Fast Fourier Transform IFFT 224 for outputas an OFDM OTA transmission (TX) 226 to be received by the adaptiveloading receiver 204. The transmission 226 may be transmitted as aconcatenated class of OFDM symbols that may result in a packet length intime in order to avoid decoder delays.

At the adaptive loading receiver 204 a decoder 228 anticipates theadaptive loading by determinatively employing an algorithm similar tothat used by the adaptive loading transmitter 202 in that it has thebenefit of the same CSI. With regard to the medium access control (MAC)layer, the MAC may handle a continuous set of possible data rates whilethe physical (PHY) layer may calculate the average data rate at a giveninstant in time and submit this information to the MAC.

For OFDM modulation with a large number of sub-carriers, such asUltra-Wide Band (UWB), savings in device complexity, size, powerconsumption and cost may be significantly made by scaling back hardwarerequirements from a full frame buffer. However, the introduction ofinter-class boundaries during modulation may inflict performancedegradation, especially when targeting an operation close to throughputmean performance.

It should be appreciated, with the benefit of the present disclosure,that the class distribution and buffer size per class might be readilycalculated, especially in UWB where the power per tone is constant.Alternatively, generally known algorithms may be employed for classdistributions and sizes, especially for applications in which the powermay change.

As discussed below, a number of performance enhancements may mitigate orenhance the communication system 200 beyond any performance detrimentsthat may be introduced by the simplified hardware architecture. Inaspects of the design, the inter-class boundary mitigation techniques216 include:

-   a technique 232 for processing an entire class per symbol technique,-   a technique 234 for using a highest quality class “Z” as a    transition class,-   a technique 236 for use of a bottom class as a transition class,-   a technique 238 for taking bits from another class when needed for    additional transitions and collapsing the remainder into a lower    class,-   a technique 240 for increasing receiver (RX) CSI feedback,-   a technique 242 for determining boundary classes,-   a technique 244 for employing receiver (RX) feedback as to the best    tones for a class prior to quantization for use at transitions, and-   a technique 246 for performance back off to mitigate inter-class    boundary effects.

Inter-Class Boundary Mitigation

Inter-class boundary occurs when less than an entire OFDM frame isbuffered. For example, say there are a total of eight (8) classesdefined in the communication system 200 numbered 0-7, and that thelowest class 0 has poorer SINR associated with it than the other classesand class 7 has the higher SINR. In an aspect of the design, the SINRsteps between the classes may be 2 or 3 dB steps. To have an entireframe buffered, for example, all of a class must be encoded and then theencoded bits must be mapped onto all the sub-carriers of all the OFDMsymbols. Next, it is necessary to proceed to the next class, and so on.In other words, one code rate is processed at a time. However, forhardware reduction purposes, it may be necessary to avoid any bufferingor to limit the size of the buffering. When the buffer size is limiteddata from more than one class may be mapped to an OFDM symbol, whichresults in boundaries between classes. Boundaries between classes aregenerally avoided because the codes are not optimized for sudden changesin data rate. As an example of changing data rates, the input of thedecoder 228 may be a block at rate ¾, followed by a block at rate 1/12,and then followed by a block at rate ⅔. In an aspect of the design, thedecoder 228 is a Viterbi decoder.

If boundary reduction is necessary, an entire class may be processedusing the technique of processing the class per symbol 232, which isused for processing an entire class per OFDM symbol before moving ontothe next class. In an aspect of the design, this may be accomplished byproceeding in reverse order of the classes for the following OFDMsymbol:

-   (1) First OFDM symbol:

(a) Class 0 (process it entirely);

(b) Class 1;

(c) . . .

(d) Class 7

-   (2) Second OFDM symbol:

(a) Class 7 (restart from last class of previous symbol to minimizeboundaries);

(b) . . .

(c) Class 1

(d) Class 0

etc.

Boundaries may be further reduced by simply increasing the size of theclass buffers. Two (2) or three (3) OFDM symbols worth of rate adaptedbits may be buffered for each class. A class buffer may be filled beforemoving onto the next class. Part of the buffer may be carried on to thenext OFDM symbol.

In some instances, boundaries may actually play a beneficial role. Forexample, since class 7 may contain very strong sub-carriers, it may bedesirable to interleave class 7 with weaker classes to give them aboost. Likewise, interleaving class 0 with other classes reduces itsweakness. Interleaving of classes may be simply achieved by having ashort buffer and by scheduling the multiplexing: e.g., class 0 comesafter class 7 if it has bits available.

In an aspect of the design, a reduction in the degradation inperformance, perhaps even a gain in performance, may be accomplishedthrough the use of the technique class Z transition 234. The class Ztransition uses the highest quality class as a transition class. Inparticular, a short transition class Z may be inserted between classes.For example, there may be a transition state between class 5 and class3. Class Z, being the highest quality class, may contain very highquality tones. However, because the tones are grouped into a limitedamount of classes (e.g. quantization and saturation), all of these greatquality tones may end up in a unique class Z. It should be appreciatedthat, with the benefit of the present disclosure, there would not besaturation when 1024 QAM is used, but anything above 64 QAM, forexample, will have to be saturated to 64 QAM. Consequently, class Z mayoften contain excellent quality tones that, once inserted between class5 and 3, may more than compensate for the loss in performance due tointer-class boundaries. In an aspect of the design, class Z has a totalof seven (7) bits, and may cover transitions between eight (8) classes.

In another aspect of the design, the technique of bottom classtransition 236 may be used. The transition class in this instance may bethe bottom class or one of the classes that uses heavy repetition. Theclasses that use heavy repetition may be well suited for transitions,because they may not suffer as much from puncturing issues.

In yet another aspect, the technique of take bits/collapse class 238 maybe used. In this aspect, if there are not enough transition bits thensome bits may be chosen from some classes and collapsed onto the lowerclass. Although a small loss of throughput may be observed, these bitsmay have excellent quality and may be used for transition.

Another aspect of the design may be to use the technique of increased RXCSI feedback 240. Increased RX CSI feedback 240 adds more feedbackinformation from the RX to the TX. The RX may, after quantizing thetone's quality into classes, check which of the tones happen to fallnear the top edge of their class (almost falling into the upper class).These tones may have, for example, one (1) or two (2) dB betterperformance than the class average. Those special bits may then be usedfor transitions. The RX feeds back to TX the location of those tones,which often happen to be adjacent so the amount of OTA resourcesconsumed for such feedback may be small.

In another aspect of the design, the technique of determine boundaryclasses 242 may be used. In this technique classes are selected that mayintersect conveniently with each other, mindful that a class mayterminate at different puncturing states. For each termination state, anext best class may be selected.

In yet another aspect of the design, the technique of RX feedback besttones/class 244 may be used. In this technique, the adaptive loadingreceiver 204 remembers, per class, the best tone before quantization.The adaptive loading transmitter 202 is informed of the next best tone,such as utilizing a specific CSI report 256. Then, the adaptive loadingtransmitter 202 uses this best tone per class as the first tone to startwith in the class. Thereby, the boundary between classes may be improveddue to additional power at the boundaries. The increased performance mayoutweigh the impact of requiring more CSI feedback.

In another aspect, the technique of performance backoff 246 may be used.Performance backoff causes a back off throughput performance to obviateboundary degradation. This back off may simply be accomplished throughthe use of the minimum level in each class rather than the mean. In thisinstance, there may be no boundary between classes and no interleavingmay be needed either. The performance backoff technique 246 may be verysimple and inexpensive to implement.

With regard to robustness, adaptive loading may push the limit of thesystem to the edge. Therefore, the system may be less robust to suddenchanges in the RF environment. The use of additional link margin mayincrease robustness. Alternatively, quick feedback and retransmissionsmay help mitigate changes in the RF environment.

Combining Puncturing and Repetition

It may be inconvenient and inefficient to use the generally known timeand frequency domain spreading of UWB. Instead, in an aspect of thedesign, a more efficient method of simple repetition before puncturingmay be used that may achieve up to 0.6 dB of gain. In this aspect, thepuncturing patterns change. Examples of the rates andrepetition/puncturing patterns are provided in Table-1. Furtheroptimization may be achieved depending upon the dB delta betweenclasses.

TABLE 1 Class Rate Encoder Repetition Puncturing 0 1/12 ⅓ 4 0 1 ⅛ ⅓ 3 1every 9 2 ⅕ ⅓ 2 1 every 6 3 ¼ ⅓ 2 2 every 6 4 ⅓ ⅓ 1 0 5 ½ ⅓ 1 1 every 36 ¾ ⅓ 1 1 every 4 7 1 ⅓, or 1 1 2 every 3, or 0

It may be seen from Table-1 that time and frequency domain spreading hasbeen replaced by repetition prior to puncturing. This may result insimpler puncturing and higher gains. It also may result in relativelysimilar puncturing patterns across the various classes, i.e., the three(3) polynomials of the encoder are nearly equally loaded, which mayreduce the effect of inter-class boundary, for example, in a Viterbidecoder.

In general, a fixed convolutional encoder with rate ⅓ punctures thenrepeats as needed to achieve various data rates; puncturing is appliedfirst, followed by repetition in the form of time and frequency domainspreading. However, this conventional method is sub-optimal as comparedto applying repetition first and then puncturing. The improvement mayaffect the rates that have time and/or frequency domain spreading (i.e.,repetition) as well as puncturing.

The gains that may be achieved are approximately 0.25 dB for 80 or 160Mbps rates and approximately 0.6 dB for 200 Mbps rate. Additional gainmay be obtained for the data rates of 53.3, 80, 106.7, 160 and 200 Mbpssince the frequency spreading and time spreading methods are not optimalin terms of frequency diversity. Certain repeated tones are transmittedin the same region that may entirely fade. This mainly involves thetones near DC that already suffer from the DC removal filter at thereceiver side.

Some of the hardware advantages of the disclosed aspects may be thefollowing way: puncturing and repetition are simpler to implement thanfrequency and time spreading. In addition, puncturing and repetition mayfurther eliminate the need for interleaver blocks such as the cyclicshift. A unique interleaver of 1200 bits may suffice, since there may beno need to support 300 and 600 Mbps, thereby simplifying thearchitecture. However, it should be appreciated, with the benefit of thepresent disclosure, that if the modes above 200 Mbps are not supported,then the device could use an interleaver of just 600 bits.

In Table-2, a comparison between current patterns and the combinedpuncturing/repetition patterns and an aspect of the design areillustrated. A “0” in the pattern means punctured bit and a “non 0”means a transmitted bit. The weight of the transmitted bit is itsrepetition level: “1” means transmitted once, “2” means transmittedtwice, “3” means transmitted three times.

TABLE 2 Current Current Current Rate Puncturing Repetition EffectiveProposed Gain (Mbps) Pattern Rate Pattern Pattern (dB) 80 1 0 1 4 4 0 43 2 3 0.25 200 11000111000111 2 22000222000222 211111111111111 0.6

By way of explanation, for the case of 80 Mbps, the current puncturingpattern is 1 0 1, which means that the second convolutional polynomial(out of 3 for rate ⅓) is unused, which weakens the encoding. Afterrepetition by four (4), the output of the remaining two (2) polynomialsis repeated 4 times. However, the second polynomial is ignored. Byperforming repetition first, each output is repeated three (3) times toobtain a pattern of 3 3 3. Then the middle polynomial is punctured onceto obtain a final pattern of 3 2 3. This pattern is close to theunpunctured pattern of 3 3 3 (i.e., as if no puncturing). No spreadingin time and/or frequency domain is necessary after this operation. In anaspect of the design, for the rate 200 Mbps, the proposed puncturingpattern may be achieved by simply repeating 1 bit every 15 bits. Thus,this repetition/puncturing patterns tend to be simpler.

Sub-Carrier Interleaving

In an aspect of the design, some diversity may be desirable to handle asudden interferer that appears on some adjacent sub-carriers byinterleaving within one (1) or two (2) OFDM symbols. Thereby, correlatedcoded bits are not carried by adjacent sub-carriers. Interleaving may bedone inside a class' buffer by shuffling the coded bits. Alternatively,interleaving may be performed by shuffling inside the tone mapper 222.Simple shuffling may result in some form of randomization (i.e.,non-deterministic interleaving). For example, when a frame is lost, itsretransmitted version may use a different shuffling pattern to avoidhitting the same weak spot twice.

Carrier Quality Classes

The adaptive loading receiver 204 measures the quality of eachsub-carrier (e.g., SINR, C/I, SNR). This may be performed in variousways. For example, it may be done through the use of an existingpreamble, a training sequence, a pilot signal, or data. In an aspect ofthe design, the receiver 204 obtains a sub-carrier's SINR and classifiesit into the appropriate class. Eight (8) possible classes may bedefined, from 0 to 7. The delta in SINR between classes could be 2 to 3dB. Class 0 could mean lowest quality and class 7 could mean highestquality. A good choice of the classes depends on the coding and optimumrepetition and/or puncturing patterns. The classes 1 to 6 may bedelimited to a size of 2 to 3 dB. However, class 0 may be unlimited onthe lower side while class 7 may be unlimited on the upper side. Thismeans that carriers in class 0 may be exceedingly weak. Class 0 maysignal “do not use these sub-carriers”. Class 7, on the other hand, maycontain exceedingly strong carriers.

Feedback to Transmitter

The adaptive loading receiver 204 may advantageously and efficiently usevaluable OTA resources and conserve battery power while enhancing OFDMtransmission by having a CSI component 248, capable of various types ofCSI reports 250 in order to provide feedback to the adaptive loadingtransmitter 202. In an aspect of the design, this feedback may be in theform of a full CSI bitmap 252, a of change sub-carriers CSI report 254,or a specific sub-carrier CSI report 256.

With further reference to FIG. 3, in an aspect of the design, theadaptive loading receiver 204 sends a feedback message 250 with three(3) bits per carrier to the adaptive loading transmitter 202. InOFDM-based UWB, there are 100 carriers per band. Thus, 300 bits per bandare needed, and 900 bits are needed for a total of three (3) bands. Thefeedback message 250 consists of a bitmap with three (3) bits percarrier. This message, which may be the report 254, may be sentinfrequently when quality levels change. Moreover, the message 250 maybe compressed. For example, this may be report 254, wherein if only afew sub-carriers are affected by a change, then a special message mayconvey the new classes for the few sub-carriers without resending theentire bitmap as in report 252. In addition, since contiguoussub-carriers often have similar quality levels, it may be possible tocompress the bitmap by encoding in the message the deltas betweenclasses rather than the absolute class number. Alternatively, ahierarchical approach may be used wherein, for a given interval, e.g.,every ten (10) contiguous tones are first assigned to a unique classthen, if needed, their individual deltas are transmitted.

In another aspect of the design, additional messages could carryspecific information for specific carriers as in report 256. Forexample, the message “do not use sub-carrier number 80” could mean thata strong fade or a strong interferer on that sub-carrier (very weakSINR) is present.

In the event where each transmitted frame is not acknowledged by a peerunit, the feedback information may go out of synchronization between theadaptive loading transmitter 202 and receiver 204. In this situation, asimple protocol may ensure that both sides know the state of the system.The adaptive loading receiver 204 may send a transaction number and theadaptive loading transmitter 202 may embed this transaction number in aheader. The transaction number in the header may inform the adaptiveloading receiver 204 of the class's state. A double buffering of theclasses at the adaptive loading receiver 204 may be used to process oldpackets before the new scheme is established.

FIG. 4 illustrates a more detailed block diagram of a wirelesscommunication system 700 that may be used to operate the various aspectsdisclosed. The communication system comprises a transmitter system 710(also known as the access point) and a receiver system 750 (also knownas access terminal). At the transmitter system 710, traffic data for anumber of data streams is provided from a data source 712 to a transmit(TX) data processor 714.

In an aspect, each data stream is transmitted over respective transmitantenna. TX data processor 714 formats, codes, and interleaves thetraffic data for each data stream, based on a particular coding schemeselected for that data stream to provide coded data. TX data processor714 may comprise the encoders 108 and 208, rate adapters 112 and 217a-c, optional interleaver 114, de-multiplexer 212, and buffer 218 asdescribed above in FIGS. 2 and 3.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped), basedon a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 730. Processor 730 may also comprisethe mapper 110 b, tone mapper 222, and the class selector 214 asdescribed above in FIGS. 2 and 3.

The modulation symbols for all data streams are then provided to a TXMIMO processor 720, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 720 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 722 a through 722 t. The TXMIMO processor 720 may also apply beamforming. TX MIMO processor 720 maycomprise the modulator 116, tone mapper 222, mapper 10 b, IFFFT 118 and224 as described above in FIGS. 2 and 3.

Each transceiver 722 a-t receives and processes a respective symbolstream to provide one or more analog signals, and further conditions(e.g., amplifies, filters, and upconverts) the analog signals to providea modulated signal suitable for transmission over the MIMO channel.N_(T) modulated signals from transceiver 722 a-t are then transmittedfrom N_(T) antennas 724 a through 724 t, respectively.

At receiver system 750, the transmitted modulated signals are receivedby N_(R) antennas 752 a through 752 r and the received signal from eachantenna 752 is provided to a respective transceiver 754 a through 754 r.Each transceiver 754 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 760 then receives and processes the N_(R) receivedsymbol streams from N_(R) transceiver 754, based on a particularreceiver processing technique to provide N_(T) “detected” symbolstreams. The RX data processor 760 then demodulates, deinterleaves, anddecodes each detected symbol stream to recover the traffic data for thedata stream. RX data processor may comprise the de-mapper 126, the FFT124, the demodulator 128, the deinterleaver 130, rate adapter 132, anddecoder 134 and 228 as described above in FIGS. 2 and 3. The processingby RX data processor 760 is complementary to that performed by TX MIMOprocessor 720 and TX data processor 714 at transmitter system 710.

The RX processor 770 may comprise the CSI 248 as described above in FIG.3. The reverse link message may comprise various types of informationregarding the communication link or the received data stream. Thereverse link messages may comprise the CSI reports as described above inFIGS. 2 and 3. The reverse link message is then processed by a TX dataprocessor 738, which also receives traffic data for a number of datastreams from a data source 736 and information from processor 770, ismodulated by a modulator 780, is conditioned by transceivers 754 athrough 754 r, and is transmitted back to transmitter system 710.

At transmitter system 710, the modulated signals from receiver system750 are received by antennas 724, conditioned by transceivers 722,demodulated by a demodulator 740, and processed by a RX data processor742 to extract the reserve link message transmitted by the receiversystem 750. Memory 772 and 732 support the processors 770 and 730respectively.

FIG. 5 illustrates a process for transmitting adaptive loaded data in anaspect of the design. First sub-carriers may be grouped according to aclass 502. The classes may be categorized based on feedback. Next,encoded data bits may be de-multiplexed according to the classes 504.Each class may have an associated data rate. The de-multiplexing alsomay rate adapt the encoded data bits in order to have the encoded databit's rate match those of the class' associated data rate. Optionally,the encoded data bits may also be interleaved. Then the rate adapteddata bits may be buffered according to their class 506. Each class mayhave an associated buffer. Finally, the buffered data is mapped onto thecorresponding groups of sub-carriers 508 for data transmission.

FIG. 6 illustrates a process for receiving data that was adaptivelyloaded in an aspect of the design. First, OFDM symbols may be de-mappedfrom sub-carriers in order to produce rate adapted data bits 602. Priorto, or after, the sub-carriers may be grouped into classes based uponthe channel state information 604. The de-mappped rate adapted data bitsmay then buffered according to their class 606. Each class has anassociated buffer. Finally, the buffered rate adapted data bits aremultiplexed in order to produce encoded data bits 608. The multiplexingalso may perform rate adaption in order to match the class' rate to theencoded data bits rate. Optionally, the encoded data bits may also bede-interleaved.

FIG. 7 illustrates an example of an apparatus that performs adaptiveloading for transmission with an aspect of the design. Transmitter 800may include a grouping module 802 configured to group the sub-carriersinto classes. The grouping may be based upon feedback received by thereceiving module 812. Transmitter 800 may include an optionalinterleaver 810 that may interleave some of the encoded data bits.Transmitter 800 may include a de-multiplexing module 804 thatde-multiplexes encoded data bits in order to correspond to the classesby rate adapting them. Transmitter 800 may include a buffering module806 that may buffer the rate adapted data bits to correspond to theirclasses. Transmitter 800 may also include a mapper module 808 that maymap the buffered data onto corresponding sub-carriers.

FIG. 8 illustrates an example of an apparatus that receives informationtransmitted by an adaptive loading transmitter with an aspect of thedesign. Receiver 900 may include a de-mapping module 902 that may de-mapOFDM symbols from sub-carriers. Receiver 900 may include a groupingmodule 904 that may group the various sub-carriers into classes.Receiver 900 may include a transmitting module 910 that can transmitchannel state information (CSI). Receiver 900 may include a bufferingmodule 906 that may buffer rate adapted data bits according to theirclass. Receiver 900 may also include a multiplexing module 908 that maymultiplex the buffered rate adapted data bits corresponding to theirclass. The multiplexing module 908 may rate adapt the buffered rateadapted bits in order to produce encoded data bits. Receiver 900 canoptionally include a de-interleaver module 912 for de-interleaving someof the encoded data bits.

Those skilled in the art would further appreciate that the variousillustrative logical blocks, modules, and steps described in connectionwith the aspects disclosed herein may be implemented as hardware,software, firmware, or any combination thereof and hardwareimplementation may be digital, analog or both. To clearly illustratethis interchangeability of hardware and software, various illustrativecomponents, blocks, modules, and steps have been described abovegenerally in terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.Skilled artisans may implement the described functionality in varyingways for each particular application, but such implementation decisionsshould not be interpreted as causing a departure from the scope of thisdisclosure.

The various illustrative logical blocks, and modules described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, anintegrated circuit, one or more microprocessors in conjunction with aDSP core, or any other such configuration.

An exemplary storage medium is coupled to the processor such theprocessor could read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

The steps or functions of a method or algorithm described in connectionwith the aspects disclosed herein may be embodied directly in hardware,in software executed by a processor, or in a combination of the two. Thesteps or functions could be interchanged without departing from thescope of the aspects.

If the steps or functions are implemented in software, the steps orfunctions may be stored on or transmitted over as one or moreinstructions of code on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any media that facilitates transfer of a computer program fromone place to another. A storage media may be any available media thatcould be assessed by a general purpose or special purpose computer. Byway of example, and not limitation, such computer-readable media couldcomprise RAM, flash memory, ROM, EPROM, EEPROM, registers, hard disk, aremovable disk, a CD-ROM, optical disk storage, magnetic disk storage,magnetic storage devices, or any other medium that may be used to carryor store desired program code means in the form of instructions or datastructures and that may be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source, using a coaxial cable, fiber opticcable, twisted pair, digital subscriber line (DSL), or wirelesstechnologies such as infrared, radio, and microwave, then the coaxialcable, fiber optic cable, twisted pair, digital subscriber line (DSL),or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically. A computerprogram product would also indicate materials to package the CD orsoftware medium therein. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the certain aspects is provided to enableany person skilled in the art to make or use the invention. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects without departing from the scope of this disclosure. Thus,this disclosure is not intended to be limited to the aspects shownherein but is to be accorded the widest scope consistent with theprinciples and novel features disclosed herein.

What is claimed is:
 1. A method for adaptive loading in an orthogonalfrequency division multiplexing (OFDM) communication system, comprising:grouping sub-carriers into at least one of a plurality of classes,wherein the grouping is based upon feedback, and wherein each class hasan associated data rate; de-multiplexing encoded data bits, sized lessthan an OFDM frame, to correspond to the at least one of a plurality ofclasses, wherein the encoded data bits are rate adapted in order tocorrespond to the class' associated data rate; buffering the rateadapted data bits according to the at least one of a plurality ofclasses, wherein each class has an associated buffer; performinginter-class boundary mitigation on the buffered rate adapted data bitsby selecting one or more of the following: processing an entire classper symbol, using a highest quality class “Z” as a transition class, usea bottom class as a transition class, taking bits from another classwhen needed for additional transitions and collapsing the remainder intoa lower class, increasing receiver (RX) CSI feedback, determiningboundary classes, employing receiver (RX) feedback as to the best tonesfor a class prior to quantization for use at transitions, andperformance back off to mitigate inter-class boundary effects; andmapping the buffered data onto the corresponding group of sub-carriersfor data transmission.
 2. The method of claim 1, further comprisinginterleaving at least some of the encoded data bits.
 3. The method ofclaim 1, wherein the buffering the rate adapted data bits comprises:utilizing discrete buffers for each one of the associated buffers. 4.The method of claim 1, wherein the feedback is a channel stateinformation (CSI) report.
 5. The method of claim 4, wherein the channelstate information (CSI) report is at least one selected from the groupconsisting of: full CSI bitmap, changed CSI, and specific CSI.
 6. Themethod of claim 4, wherein the channel state information (CSI) reportcomprising three bits per sub-carrier.
 7. The method of claim 1, whereinthe at least one of a plurality of classes comprises eight classesnumbered as integers zero through seven.
 8. The method of claim 1,wherein the rate adaption comprises: performing repetition on theencoded data bits first then puncturing the result.
 9. The method ofclaim 1, wherein the mapping comprises utilizing a dynamic look up tableresiding in a random access memory (RAM) or registers.
 10. An apparatusfor adaptive loading in an orthogonal frequency division multiplexing(OFDM) communication system, comprising: means for grouping sub-carriersinto at least one of a plurality of classes, wherein the grouping isbased upon feedback, and wherein each class has an associated data rate;means for de-multiplexing encoded data bits, sized less than an OFDMframe, to correspond to the at least one of a plurality of classes,wherein the encoded data bits are rate adapted in order to correspond tothe class' associated data rate; means for buffering the rate adapteddata bits according to the at least one of a plurality of classes,wherein each class has an associated buffer; means for performinginter-class boundary mitigation on the buffered rate adapted data bitsby selecting one or more of the following: processing an entire classper symbol, using a highest quality class “Z” as a transition class, usea bottom class as a transition class, taking bits from another classwhen needed for additional transitions and collapsing the remainder intoa lower class, increasing receiver (RX) CSI feedback, determiningboundary classes, employing receiver (RX) feedback as to the best tonesfor a class prior to quantization for use at transitions, andperformance back off to mitigate inter-class boundary effects; and meansfor mapping the buffered data onto the corresponding group ofsub-carriers for data transmission.
 11. The apparatus of claim 10,further comprising: means for interleaving at least some of the encodeddata bits.
 12. The apparatus of claim 10, wherein the means forbuffering the rate adapted data bits comprises: means for utilizingdiscrete buffers for each one of the associated buffers.
 13. Theapparatus of claim 10, further comprising: means for receiving feedback,and wherein the feedback is a channel state information (CSI) report.14. The apparatus of claim 13, wherein the channel state information(CSI) report is at least one selected from the group consisting of: fullCSI bitmap, changed CSI, and specific CSI.
 15. The apparatus of claim13, wherein the channel state information (CSI) report comprising threebits per sub-carrier.
 16. The apparatus of claim 10, wherein the atleast one of a plurality of classes comprises eight classes numbered asintegers zero through seven.
 17. The apparatus of claim 10, wherein therate adaption comprises: means for performing repetition on the encodeddata bits first then puncturing the result.
 18. An apparatus foradaptive loading in an orthogonal frequency division multiplexing (OFDM)communication system, comprising: a grouping module configured to groupsub-carriers into at least one of a plurality of classes, wherein thegrouping is based upon feedback, and wherein each class has anassociated data rate; a de-multiplexing module configured tode-multiplex encoded data bits, sized less than one OFDM frame, tocorrespond to the at least one of a plurality of classes, wherein theencoded data bits are rate adapted in order to correspond to the class'associated data rate; a buffering module configured to buffer the rateadapted data bits according to the at least one of a plurality ofclasses, wherein each class has an associated buffer; the bufferingmodule configured to perform inter-class boundary mitigation on thebuffered rate adapted data bits by selecting one or more of thefollowing: processing an entire class per symbol, using a highestquality class “Z” as a transition class, use a bottom class as atransition class, taking bits from another class when needed foradditional transitions and collapsing the remainder into a lower class,increasing receiver (RX) CSI feedback, determining boundary classes,employing receiver (RX) feedback as to the best tones for a class priorto quantization for use at transitions, and performance back off tomitigate inter-class boundary effects; and a mapper module configured tomap the buffered data onto the corresponding group of sub-carriers fordata transmission.
 19. The apparatus of claim 18, further comprising: aninterleaving module configured to interleave at least some of theencoded data bits.
 20. The apparatus of claim 18, further comprising: areceiving module configured to receive feedback, and wherein thefeedback is a channel state information (CSI) report.
 21. The apparatusof claim 18, wherein the at least one of a plurality of classescomprises eight classes numbered as integers zero through seven.
 22. Theapparatus of claim 18, wherein the de-multiplexing module is furtherconfigured to perform repetition on the encoded data bits first thenpuncture the result.
 23. A computer program product comprising anon-transitory computer-readable storage device comprising: code forcausing a computer to group sub-carriers into at least one of aplurality of classes, wherein the grouping is based upon feedback, andwherein each class has an associated data rate; code for causing acomputer to de-multiplex encoded data bits, sized less than oneorthogonal frequency division multiplexing (OFDM) frame, to correspondto the at least one of a plurality of classes, wherein the encoded databits are rate adapted in order to correspond to the class' associateddata rate; code for causing a computer to buffer the rate adapted databits according to the at least one of a plurality of classes, whereineach class has an associated buffer; code for causing a computer toperform inter-class boundary mitigation on the buffered rate adapteddata bits by selecting one or more of the following: processing anentire class per symbol, using a highest quality class “Z” as atransition class, use a bottom class as a transition class, taking bitsfrom another class when needed for additional transitions and collapsingthe remainder into a lower class, increasing receiver (RX) CSI feedback,determining boundary classes, employing receiver (RX) feedback as to thebest tones for a class prior to quantization for use at transitions, andperformance back off to mitigate inter-class boundary effects; and codefor causing a computer to map the buffered data onto the correspondinggroup of sub-carriers for data transmission.
 24. An integrated circuitfor adaptive loading in an orthogonal frequency division multiplexing(OFDM) communication system, comprising: a processor; a memory inelectronic communication with the processor, the memory storing computerexecutable instructions, that when executed by the processor, cause theprocessor to: group sub-carriers into at least one of a plurality ofclasses, wherein the grouping is based upon feedback, and wherein eachclass has an associated data rate, to receive feedback; de-multiplexencoded data bits, sized less than one OFDM frame, to correspond to theat least one of a plurality of classes, wherein the encoded data bitsare rate adapted in order to correspond to the class' associated datarate; buffer the rate adapted data bits according to the at least one ofa plurality of classes, wherein each class has an associated buffer;perform inter-class boundary mitigation on the buffered rate adapteddata bits by selecting one or more of the following: processing anentire class per symbol, using a highest quality class “Z” as atransition class, use a bottom class as a transition class, taking bitsfrom another class when needed for additional transitions and collapsingthe remainder into a lower class, increasing receiver (RX) CSI feedback,determining boundary classes, employing receiver (RX) feedback as to thebest tones for a class prior to quantization for use at transitions, andperformance back off to mitigate inter-class boundary effects; and mapthe buffered data onto the corresponding group of sub-carriers for datatransmission.